This invention relates to an optical memory playback apparatus using an electroluminescent semiconductor element.
As means for collecting and reproducing bits of information by the medium of a light beam there has, for instance, been proposed an apparatus in which the light radiated from a helium-neon laser is directed to bits of information stored in the spiral groove of a disk as in an information-storing videodisk. This apparatus has a disadvantage that it cannot effectively operate without using a relatively large light source and a relatively large optical system which enables the light from the light source to travel in the direction of the information-storing part of the disk and, upon impingement thereon, reflect in the direction of a photo-detector.
As is well known, a minute electroluminescent semiconductor device on the hundred .mu.m order is commercially available in the form of a light emitting diode or semiconductor laser. U.S. Pat. No. 3,812,477 teaches a minute semiconductor laser which is capable of reading bits of information out of a compact-storing memory with high resolution.
In the information processing system contemplated by this U.S. patent, a three-mirror resonator is constructed of an outer mirror and a laser element, whereby information stored in the form of variation in the reflection factor on the outer mirrors is read out by allowing the variation in the light output (namely the presence or absence of oscillation) of the laser element produced in consequence of the variation in the reflection factors of the outer mirrors to be detected by a separately installed photo-detector.
The signal playback system disclosed in U.S. Pat. No. 3,941,945 effects the reading of information by relying on the same operating principle and structure as the invention of the U.S. patent mentioned above, except that the laser element and the detector element are produced monolithically.
In the signal reproducing system disclosed in U.S. Pat. No. 4,005,259, when the light radiated from a semiconductor laser having an antireflection coating applied to one end surface thereof is reflected by an outer mirror back to the laser, a resonator is formed between the outer mirror and the laser. In this system the reading of information is accomplished by the photo-sensor which detects the variation in the light output which occurs when the outer mirror acquires a reflection factor high enough to cause laser oscillation.
The information processing devices disclosed in the aforementioned U.S. patents invariably require outer mirrors to function as component parts of laser resonators and, therefore, are susceptible to erroneous operation due to minute vibrations arising in these outer mirrors. Thus, as constant rigid alignment of the component parts is required to ensure perfect accuracy of operations, these devices have room for further improvement.
An object of the present invention is to provide a very minute optical memory playback apparatus possessing a greatly simplified structure.
Another object of this invention is to provide an optical memory playback apparatus which, owing to the utilization of the self-coupling effect, permits free selection of the length of the light path between the light source and the reflecting object serving as an information storage medium.
Still another object of this invention is to provide an optical memory playback apparatus which never produces an erroneous read-out.
The term "coupling effect" as herein used is defined as the phenomenon which is observed when an electroluminescent semiconductor subjected to light irradiation is undergoing changes in carrier density and changes in the course of carrier recombination, which changes either result in the pumping, quenching or extinguishing of the light output of the semiconductor or induce optical changes as in the mode or polarization of the light. The term "self-coupling effect" refers to a particular type of "coupling effect" that is brought about by the light emitted from one and the same electroluminescent semiconductor.
The term "memory playback" as herein used is defined as the act of reproducing, by opto-electronic means using an electroluminescent semiconductor element, the information stored along an information track in the form of variation in the optical characteristics of an optical storage medium.